Interesting notes on the near-ubiquity of clay consumption among many animals. For one thing, the famous "salt licks" frequented by animals like elephants and cattle might be more accurately called "clay licks". When ingested, clay can help neutralize many plant toxins.

Even more interesting is that in many less-urban, less-developed cultures, clay-eating by children and pregnant women is still relatively common - which makes sense, since children and fetuses are especially susceptible to dietary toxins. So, let your kids eat dirt! I know it's random speculation, but Barlow's mention of a potential link between the rise in childhood allergies and the fact that it's less common for first-world children to play in the dirt these days is thought-provoking.